Light emitting element and electronic device using the same

ABSTRACT

A layer included in an electroluminescent element is required to be thickened to optimize light extraction efficiency of the electroluminescent element and to prevent short-circuit between electrodes. However, in a conventional element material, desired light extraction efficiency cannot be accomplished since drive voltage rises or power consumption is increased as the element material is thickened. A composite is formed by mixing a conjugated molecule having low ionization potential and a substance having an electron-accepting property to the conjugated molecule. A composite layer included in an element is formed using the composite as an element material. The composite layer is arranged between a first electrode and a light emitting layer or between a second electrode and a light emitting layer. The composite layer has high conductivity; therefore, drive voltage does not rise even if a film thickness is increased. Thus, an electroluminescent element which can prevent short-circuit of an electrode can be provided.

TECHNICAL FIELD

The present invention relates to a light emitting element. Morespecifically, the invention relates to a light emitting element having alayer composed of a composite of a conjugated molecule and a substancehaving an electron-accepting property to the conjugated molecule.Further, the invention relates to a light emitting device including alight emitting element.

BACKGROUND ART

An electroluminescent (EL) display is one of the most remarkable devicesas a flat panel display device for the next generation, which iscomposed of a light emitting element. In a light emitting element,electrons injected from a cathode and holes injected from an anode arerecombined in a light emitting layer when current is flowed to formmolecule excitons. The light emitting element emits light by usingphotons discharged when the molecular excitons return to the groundstate. Therefore, one of conditions to manufacture a light emittingelement having favorable emission efficiency is to use whole excitationenergy of molecule excitons for light emission.

One example which meets the above condition is a multilayer structure ofa light emitting element. For example, a multilayer is formed of a holeinjecting layer, a hole transport layer, a light emitting layer, anelectron transport layer, an electron injecting layer, and the likebetween a pair of electrodes including an anode and a cathode.

Further, the effective injection of holes and electrons, which arecarriers, to a light emitting layer is also one of the conditions tomanufacture a light emitting element having favorable emissionefficiency. For that purpose, it is conventional and known that amaterial having low ionization potential is used for a hole injectinglayer and a material having high electron affinity is used for anelectron injecting layer.

Such a layer included in a multilayer structure of a light emittingelement described above is formed from metal oxide which is an inorganiccompound, or an organic compound.

In addition, an attempt to form a light emitting element using a layerin which an organic compound is mixed with an inorganic compound hasbeen made. For example, a light emitting element formed by stacking alayer formed from a material dispersed with an organic compound (a holetransporting compound, an electron transporting compound, and aluminescent compound) in a silica matrix via a covalent bond isdisclosed in the following Patent Document 1 (Patent Document 1:Japanese Patent Application Laid-Open No. 2000-306669). In the PatentDocument 1, it is reported that durability or heat-resistance of anelement is enhanced.

DISCLOSURE OF INVENTION

However, there is the following problem in the case of using metal oxideas a layer included in a light emitting element. Metal oxide is easy tocrystallize, and by the crystallization, depression/projection is formedin the surface of the metal oxide. An electric field is concentrated inthis projection and therefore a light emitting element having highreliability cannot be obtained. In addition, there is another problemthat drive voltage rises when a film thickness of metal oxide isincreased for the purpose of preventing short-circuit between electrodesof a light emitting element due to dust or the like or for the purposeof optical design that light from a light emitting layer is efficientlyextracted.

On the other hand, in the case of using an organic compound as a layerincluded in a light emitting element, drive voltage rises since holesare difficult to go into the organic compound If a material having a lowwork function is used as an anode. Therefore, it is not preferable touse a material having a low work function as an anode, so there is alimitation on an anode material. In addition, there is another problemthat drive voltage rises when a film thickness is increased in a similarway to the above metal oxide material.

Further, in a light emitting element disclosed in the above PatentDocument 1, organic compounds are simply dispersed in metal oxide havingan insulating property; therefore, current is made to be difficult toflow compared with a conventional light emitting element (in otherwords, voltage which is required to flow a certain amount of current isincreased). That is, only current having low density flows. Therefore,in the structure disclosed in the Patent Document 1, drive voltage risesor power consumption is increased even though durability orheat-resistance is obtained.

In addition, when a film thickness is increased in the structure shownin the Patent Document 1, the rising of drive voltage is made to befurther apparent. That is, it is practically difficult to increase afilm thickness in the structure disclosed in the Patent Document 1.

FIG. 14 is a conventional light emitting element disclosed in the abovePatent Document 1, in which a layer 1503 formed from a materialdispersed with an organic compound in a silica matrix is interposedbetween a first electrode (anode) 1501 and a second electrode (cathode)1502. That is, although the layer 1503 is entirely formed from a silicamatrix, reference numeral 1511 denotes a hole transport layer formedfrom a material dispersed with a hole transporting compound in a silicamatrix, reference numeral 1513 denotes an electron transport layerformed from a material dispersed with an electron transporting compoundin a silica matrix, and reference numeral 1512 denotes a light emittinglayer formed from a material dispersed with a luminescent compound in asilica matrix. It is considered that, when voltage is applied to thiselement, holes and electrons are injected from the first electrode(anode) 1501 and the second electrode (cathode) 1502, respectively, andthen recombined with each other in the light emitting layer 1512,thereby the luminescent compound emits light.

Although carrier transport in this element is conducted by the holetransport layer 1511 or the electron transport layer 1513, there is aproblem that current is difficult to flow since an organic compound isdispersed in an insulating silica matrix. For example, in the holetransport layer 1511, a hole moves by hopping among hole transportingcompounds existing in the hole transport layer 1511; therefore, a silicamatrix having an insulating property is uninvolved in hole transporting.On the contrary, the silica matrix prevents a hole from hopping. This isapplicable to the electron transport layer 1513. Therefore, drivevoltage obviously rises compared with a conventional light emittingelement.

It is an object of the invention to provide a light emitting elementwhich operates at low drive voltage. It is another object of theinvention to provide a light emitting element having high reliability.It is still another object of the invention to provide a light emittingelement which can easily prevent short-circuit between electrodes. It isstill more another object of the invention to provide a light emittingelement having high light extraction efficiency. It is still furthermore another object of the invention to provide a light emitting elementhaving a high hole injecting property or a high hole transportingproperty.

As a result of diligent study, the inventors have finally found out thatthe object can be achieved by arranging a layer (hereinafter, referredto as composite layer) composed of a composite of any of conjugatedmolecules represented by general formulas [1] to [5] (hereinafter,referred to as conjugated molecule) and a substance having anelectron-accepting property to this conjugated molecule (hereinafter,referred to as electron-accepting substance) between at least one of apair of electrodes and a light emitting layer placed between the pair ofelectrodes.

It is preferable to use metal oxide or metal nitride as theelectron-accepting substance, more preferably, oxide having a transitionmetal which belongs to any one of Groups 4 to 12 in the periodic table.Of the transition metal oxides, many oxides each having a transitionmetal which belongs to any one of Groups 4 to 8 have highelectron-accepting properties. In particular, vanadium oxide, molybdenumoxide, rhenium oxide, tungsten oxide, ruthenium oxide, titanium oxide,chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, andniobium oxide are preferred.

Further, an organic compound having an electron-accepting property maybe used as the electron-accepting substance. Specifically,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethan (F4-TCNQ),chloranil, and the like are given. Further, Lewis acid may be used asthe electron-accepting substance. As an example of Lewis acid, FeCl₃(iron chloride (III)) and AlCl₃ (aluminum chloride) are given.

The most suitable mixture ratio of the electron-accepting substance inthe composite layer to any of the conjugated molecules represented bygeneral formulas [1] to [5] is as follows: an electron-acceptingsubstance/conjugated molecule=0.1 to 10, preferably 0.5 to 2, at a molarratio. At this mixture ratio, an electron is efficiently transferredbetween the electron-accepting substance and the conjugated molecule andthe highest conductivity of the composite layer is obtained.

wherein X is the same as or different from Z, and X and Z each representany of a sulfur atom, an oxygen atom, a nitrogen atom to which hydrogen,an alkyl group, or an aryl group is bonded, or a silicon atom to whichhydrogen, alkyl group, or an aryl group is bonded; Y represents anarylene group; and R¹ to R⁶ each represent any of hydrogen, an arylgroup, an alkyl group, a cyano group, a dialkylamino group, a thioalkoxygroup, and an alkoxy group.

wherein Y represents an arylene group, and R¹ to R⁶ each represent anyof hydrogen, an aryl group, an alkyl group, a cyano group, adialkylamino group, a thioalkoxy group, and an alkoxy group.

wherein Y represents an arylene group, and R¹ to R⁶ each represent anyof hydrogen, an aryl group, an alkyl group, a cyano group, adialkylamino group, a thioalkoxy group, and an alkoxy group.

wherein Y represents an arylene group; R¹ to R⁶ each represent any ofhydrogen, an aryl group, an alkyl group, a cyano group, a dialkylaminogroup, a thioalkoxy group, and an alkoxy group; and R⁷ and R⁸ eachrepresent any of hydrogen, an alkyl group, and an aryl group.

wherein Y represents an arylene group; R¹ to R⁶ each represent any ofhydrogen, an aryl group, an alkyl group, a cyano group, a dialkylaminogroup, a thioalkoxy group, and an alkoxy group; and R⁷ to R¹⁰ eachrepresent any of hydrogen, an alkyl group, and an aryl group.

As for the conjugated molecules represented by the above generalformulas [1] to [5], in the formula, Y represents an arylene group andrepresents a bivalent aromatic hydrocarbon radical having a carbonnumber of 6 to 20 or a bivalent heteroaromatic ring radical having acarbon number of 4 to 30 including oxygen, nitrogen, sulfur, or silicon.

As for the conjugated molecules represented by the above generalformulas [1] to [5], in the formula, a cyclic structure is formed by R¹and R² and a cyclic structure is formed by R³ and R⁴.

One embodiment of the invention comprises a pair of electrodes formed ofa first electrode and a second electrode; a light emitting layer betweenthe electrodes; a first layer between the first electrode and the lightemitting layer; and a second layer between the second electrode and thelight emitting layer, wherein the first layer or the second layerincludes a composite layer of an electron-accepting substance and any ofthe conjugated molecules represented by general formulas [1] to [5].

In the above embodiment, the composite layer may be arranged so as to bein contact with the first electrode or may be arranged so as to be incontact with the light emitting layer in the first layer. The compositelayer may be arranged so as to be in contact with the second electrodeor may be arranged so as to be in contact with the light emitting layerin the second layer.

In the above embodiment, both of the first layer and the second layermay include the composite layer. In a light emitting element in whichlight is emitted from the light emitting layer when voltage is appliedto the electrode so that an electric potential of the first electrode ishigher than an electric potential of the second electrode, an electrongeneration layer is provided at a light emitting layer side so as to bein contact with the composite layer in the case where the compositelayer is included in the second layer.

The term “composite layer” in this specification means a layer formed byusing a composite of any of conjugated molecules represented by generalformulas [1] to [5] described above and a substance having anelectron-accepting property to the conjugated molecule.

The conjugated molecules represented by the general formulas [1] to [5]is obtainable by introducing any two skeletons of a thiophene skeleton,a furan skeleton, a pyrrol skeleton, and a silole skeleton which areelectron abundant aromatic rings having low ionization potential into aconjugated molecule such as a phenylene ring. The conjugated molecule isexpected to have low ionization potential. In particular, when R¹ to R⁶are substituents having an electron-donating property such as an alkoxygroup, it is possible to provide a conjugated molecule having furthersmaller ionization potential. By mixing such a conjugated molecule withan electron-accepting substance, a composite layer is obtained, andaccordingly, an electron is transferred between the conjugated moleculeand the electron-accepting substance. In other words, a hole based onionization potential of a conjugated molecule is already generated inthe composite layer before voltage is applied to a light emittingelement.

Therefore, a light emitting element with lower hole injection barriercan be obtained by including a composite layer of the presentapplication compared with a layer formed from only a material having lowionization potential. Further, a light emitting element in which a holeis easy to move can be obtained. In terms of such a function of thecomposite layer, the composite layer of the present application has afunction like a hole generation layer or a hole transport layer in somecases.

Further, as described above, an electron is transferred even beforevoltage is applied in the composite layer employed in the presentapplication; therefore, the composite layer is a film having extremelyhigh conductivity. Thus, a light emitting element in which drive voltageand power consumption are low can be provided. In addition, drivevoltage scarcely rises in proportion to the thickening of the compositelayer; therefore, short-circuit between electrodes of a light emittingelement can be prevented by thickening the composite layer. Further,light extraction efficiency can be optimized by thickening the compositelayer. Furthermore, a light emitting element having high reliability canbe provided. In addition, a light emitting element having high emissionefficiency can be provided.

The composite layer in which a conjugated molecule is mixed with anelectron-accepting substance is difficult to be crystallized; therefore,a light emitting element with less operation failure due tocrystallization of a layer can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views showing a light emitting element according tothe present invention;

FIG. 2 is a view showing a light emitting element according to theinvention;

FIGS. 3A to 3C are views showing a light emitting element according tothe invention;

FIG. 4 is a view showing a top view of a light emitting device;

FIG. 5 is a diagram showing a circuit for making one pixel operate;

FIG. 6 is a top view of a pixel portion;

FIGS. 7A to 7C are views showing a light emitting element according tothe invention;

FIG. 8 is a view showing a passive type light emitting device accordingto the invention;

FIGS. 9A to 9C are views showing an electronic device according to theinvention;

FIG. 10 is a view showing an electronic device in which a light emittingelement according to the invention is incorporated into a backlight;

FIG. 11 is a view showing ultraviolet-visible spectrum of a conjugatedmolecule;

FIGS. 12A to 12D are views of a synthesis scheme;

FIG. 13 is a view showing ultraviolet-visible spectrum (2.55×10⁻⁵M inmethylene chloride) of a conjugated molecule; and

FIG. 14 is a view showing a conventional example.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention aredescribed in detail with reference to the drawings. However, it iseasily understood by those who are skilled in the art that embodimentsand details herein disclosed can be modified in various ways withoutdeparting from the purpose and the scope of the present invention.Therefore, it should be noted that the description of embodiments shouldnot be interpreted as limiting the present invention. Further, any ofthe embodiments and examples to be given below can be appropriatelycombined.

Embodiment 1

One mode of a light emitting element of the present invention isexplained with reference to FIGS. 1A to 1C.

FIGS. 1A to 1C show a light emitting element including a first layer 111which is in contact with a first electrode 101, a second layer 112 whichis in contact with the first layer 111, and a third layer 113 which isin contact with the second layer 112 and a second electrode 102 betweenthe first electrode 101 and the second electrode 102. In FIGS. 1A to 1C,light is emitted when voltage is applied to the electrode so that anelectric potential of the first electrode 101 is higher than an electricpotential of the second electrode 102. The second layer 112 is a lightemitting layer, and the third layer 113 is a layer having a function oftransporting or injecting an electron to the light emitting layer whichis the second layer.

The second layer 112 contains a light emitting substance. The secondlayer 112 may be a layer formed from only a light emitting substance.However, in the case of generating concentration quenching, the secondlayer 112 is preferably formed by dispersing a light emitting substanceinto a layer formed from a substance having a larger energy gap than theenergy gap of the light emitting substance. By including a lightemitting substance in the second layer 112 by dispersing, light emissioncan be prevented from quenching due to concentration. Here, the term“energy gap” means an energy gap between the LUMO level and the HOMOlevel.

The light emitting substance is not especially limited, and a substancecapable of emitting light with a desired emission wavelength and havingfavorable emission efficiency may be used. In order to obtain red lightemission, for example, the following substances exhibiting emissionspectrum with peaks at 600 nm to 680 nm can be employed as the lightemitting substance:4-dicyanomethylene-2-isopropyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(abbreviated as DCJTI);4-dicyanomethylene-2-methyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(abbreviated as DCJT);4-dicyanomethylene-2-tert-butyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(abbreviated as DCJTB); periflanthene;2,5-dicyano-1,4-bis[2-(10-methoxy-1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]benzene; or the like. In order to obtain green light emission,substances exhibiting emission spectrum with peaks at 500 nm to 550 nmsuch as N,N′-dimethylquinacridon (abbreviated as DMQd); coumarin 6;coumarin 545T; or tris(8-quinolinolato) aluminum (abbreviated as Alq₃)can be employed as the light emitting substance. In order to obtain bluelight emission, the following substances exhibiting emission spectrumwith peaks at 420 nm to 500 nm can be employed as the light emittingsubstance: 9,10-bis(2-naphthyl)-tert-butylanthracene (abbreviated ast-BuDNA); 9,9′-bianthryl; 9,10-diphenylanthracene (abbreviated as DPA);9,10-bis(2-naphthyl) anthracene (abbreviated as DNA);bis(2-methyl-8-quinolinolato)-4-phenylphenolate-gallium (abbreviated asBGaq); bis(2-methyl-8-quinolinolato)-4-phenylphenolate-aluminum(abbreviated as BAlq); or the like. As described above, in addition tosuch substances which emit fluorescence, substances which emitphosphorescence such asbis[2-(3,5-bis(trifluoromethyl)phenyl)pyridinato-N,C^(2′)]iridium(III)picolinato (abbreviated as Ir(CF₃ppy)₂(pic));bis[2-(4,6-difluorophenyl)pyridinato)-N,C^(2′)]iridium(III)acetylacetonato(abbreviated as FIr(acac));bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinato(abbreviated as FIr(pic)); or tris(2-phenylpyridinato-N,C^(2′))iridium(abbreviated as Ir(ppy)₃) can also be used as the light emittingsubstance.

Further, a substance included in the light emitting layer as well as thelight emitting substance and used in order that the light emittingsubstance is dispersed is not especially limited, and may beappropriately selected by taking into consideration that an energy gapor the like of a substance used as the light emitting substance. Forexample, an anthracene derivative such as9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviated as t-BuDNA); acarbazole derivative such as 4,4′-bis(N-carbazolyl)biphenyl (abbreviatedas CBP); a quinoxaline derivative such as 2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviated as TPAQn) or2,3-bis{4-[N-(1-naphthyl)-N-phenylamino]phenyl}-dibenzo[f,h] quinoxaline(abbreviated as NPADiBzQn); a metal complex such asbis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviated as Znpp₂) orbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviated as ZnBOX); andthe like can be used together with the light emitting substance.

In FIG. 1A, the first layer 111 includes a composite layer 114 composedof a composite formed from a conjugated molecule and anelectron-accepting substance, and a hole transport layer 115. Thecomposite layer 114 is arranged at a first electrode 101 side in thefirst layer, and the hole transport layer 115 is arranged at a secondlayer 112 side. In this structure, the composite layer 114 serves as ahole generation layer.

In general, an electrode material having a high work function is used asthe first electrode 101; however, an electrode having a low workfunction (for example, aluminum, magnesium, and the like) can be used asthe first electrode 101 when the composite layer 114 is in contact withthe first electrode 101. This is because a hole is transferred alsobetween the first electrode 101 having a low work function and thecomposite layer 114 since ionization potential of a conjugated molecule,which is a configuration factor of the composite layer 114, is extremelylow and a hole is generated in the composite layer 114.

In FIG. 1B, the first layer 111 includes a composite layer 116 composedof a composite formed from a conjugated molecule and anelectron-accepting substance, and a hole injecting layer 117. Thecomposite layer 116 is arranged at a second layer side in the firstlayer, and the hole injecting layer 117 is arranged at a first electrode101 side. In this structure, the composite layer 116 serves as a holetransport layer.

In FIG. 1C, the first layer 111 is a composite layer 118 composed of acomposite formed from a conjugated molecule and an electron-acceptingsubstance. In this structure, the composite-layer 118 serves as a holegeneration layer or a hole transport layer, or both of a hole generationlayer and a hole transport layer.

Since the composite layer is placed between the first electrode 101 andthe second layer 112 which is a light emitting layer in any ofstructures of FIGS. 1A to 1C, a light emitting element having a highhole injecting property or a high hole transporting property can beobtained. Further, a drive voltage does not rise even if a filmthickness of the composite layer is made to be increased since thecomposite layer has high conductivity. Therefore, light extractionefficiency can be optimized or short-circuit between the electrodes ofthe light emitting element can be suppressed by thickening the compositelayer. Although an example in which the composite layer is in contactwith the first electrode or the second electrode is shown in each ofFIGS. 1A and 1B, the composite layer is not necessarily in contact withthe first electrode or the second electrode. Another layer may existbetween the composite layer 114 and the first electrode 101 in FIG. 1A,and another layer may exist between the composite layer 116 and thesecond layer 112 in FIG. 1B.

In FIG. 1A, the hole transport layer 115 is a layer having a function oftransporting a hole and has a function of transporting a hole from thecomposite layer 114 to the second layer 112. The distance between thecomposite layer 114 and the second layer 112 can be extended byproviding the hole transport layer 115, and as a result, light emissioncan be prevented from quenching due to metal included in the compositelayer 114. The hole transport layer is preferably formed from asubstance having a high hole transporting property, and especially, thehole transport layer is preferably formed from a substance having holemobility of 1×10⁻⁶ cm²/Vs or more. It is to be noted that the term“substance having a high hole transporting property” means that mobilityof a hole is higher than that of an electron and a value of a ratio ofelectron mobility to hole mobility (=hole mobility/electron mobility) islarger than 100. As a specific example of a substance which can be usedfor forming the hole transport layer 115, the following substances aregiven: 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated asNPB), 4,4′-bis[N-(3-methylphenyl)-N-phenylamino] biphenyl (abbreviatedas TPD), 4,4′,4″-tris(N,N-diphenylamino) triphenylamine (abbreviated asTDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino] triphenylamine(abbreviated as MTDATA),4,4′-bis{N-[4-(N,N-di-m-tolylamino)phenyl]-N-phenylamino} biphenyl(abbreviated as DNTPD), 1,3,5-tris[N,N-di(m-tolyl)amino] benzene(abbreviated as m-MTDAB), 4,4′,4″-tris(N-carbazolyl) triphenylamine(abbreviated as TCTA), phthalocyanine (abbreviated as H₂Pc), copperphthalocyanine (abbreviated as CuPc), vanadyl phthalocyanine(abbreviated as VOPc), and the like.

In FIG. 1B, the hole injecting layer 117 is a layer having a function ofassisting the injection of a hole from the first electrode 101 to thecomposite layer 116. By providing the hole injecting layer 117, thedifference of ionization potential between the first electrode 101 andthe composite layer 116 is relieved and a hole is easy to inject. Thehole injecting layer 117 is preferably formed from a substance havinglower ionization potential than that of a substance from which thecomposite layer 116 is formed and having higher ionization potentialthan that of a substance from which the first electrode 101 is formed,or a substance that energy band is curved when the substance is formedas a thin film having a film thickness of 1 nm to 2 nm between thecomposite layer 116 and the first electrode 101. As a specific exampleof a substance which can be used for forming the hole injecting layer117, a phthalocyanine-based compound such as phthalocyanine (abbreviatedas H₂Pc) or copper phthalocyanine (CuPC); a high molecular weightmaterial such as poly(ethylenedioxythiophene)/poly(styrene sulfonate)water solution (PEDOT/PSS); and the like are given. The hole injectinglayer 117 is preferably formed so that ionization potential in the holeinjecting layer 117 is comparatively higher than ionization potential inthe composite layer 116. In the case of providing the hole injectinglayer 117, the first electrode 101 is preferably formed from a substancehaving a high work function such as indium tin oxide.

The third layer 113 may be a layer having a function of transporting orinjecting an electron injected from the second electrode 102 to a lightemitting layer which is the second layer, and the structure is notlimited. In the case where the third layer 113 includes, for example, anelectron transport layer, any layer may be generally used for theelectron transport layer as long as the electron transport layer has afunction of transporting an electron. As a material for forming theelectron transport layer, the following substances are given: metalcomplexes such as tris(8-quinolinolato) aluminum (abbreviated as Alq₃),tris(4-methyl-8-quinolinolato) aluminum (abbreviated as Almq₃),bis(10-hydroxybenzo[h]-quinolinato) beryllium (abbreviated as BeBq₂),bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviated asBAlq), bis[2-(2-hydroxyphenyl)benzoxazolato] zinc (abbreviated asZn(BOX)₂), and bis[2-(2-hydroxyphenyl)benzothiazolato] zinc (abbreviatedas Zn(BTZ)₂); 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviated as PBD);1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl] benzene(abbreviated as OXD-7);3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviated as TAZ);3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviated as p-EtTAZ); bathophenanthroline (abbreviated as BPhen);bathocuproin (abbreviated as BCP); 4,4-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviated as BzOs); and the like.

In addition, the hole transport layer 115 and the electron transportlayer of the third layer 113 may be formed from a bipolar substance. Abipolar substance is a substance in which a value of a ratio of mobilityof one carrier which is any of an electron and a hole to mobility of theother carrier is 100 or less, preferably 10 or less, when mobility ofone carrier and mobility of the other carrier are compared with eachother. As the bipolar substance, for example, 2,3-bis(4-diphenylaminophenyl) quinoxaline (abbreviated as TPAQn),2,3-bis{4-[N-(1-naphthyl)-N-phenylamino]phenyl}-dibenzo[f,h] quinoxaline(abbreviated as NPADiBzQn), and the like are given. In particular, asubstance in which mobility of a hole or an electron is 1×10⁻⁶ cm²/Vs ormore is preferably used among bipolar substances. Further, the holetransport layer 115 and the electron transport layer may be formed fromthe same bipolar substance.

In the case where the third layer 113 includes an electron generationlayer, any layer may be generally used as long as the electrongeneration layer has a function of generating an electron. The electrongeneration layer can be formed by mixing at least one substance selectedfrom a substance having a high electron transporting property or abipolar substance with a substance which shows an electron-donatingproperty to these substances. Here, in particular, a substance havingelectron mobility of 1×10⁻⁶ cm²/Vs or more is preferable among asubstance having a high electron transporting property and a bipolarsubstance. As for each of the substance having a high electrontransporting property and the bipolar substance, the above-describedsubstance can be used. At least one substance selected from alkali metalor alkaline earth metal, specifically, lithium (Li), calcium (Ca),sodium (Na), potassium (K), magnesium (Mg), or the like can be used. Inaddition, alkali metal oxide or alkaline earth metal oxide, alkali metalnitride, alkaline earth metal nitride, alkali metal fluoride, alkalineearth metal fluoride, or the like, specifically, lithium oxide (Li₂O),calcium oxide (CaO), sodium oxide (Na₂O), potassium oxide (K₂O),magnesium oxide (MgO), magnesium nitride (Mg₃N₂), lithium fluoride(LiF), cesium fluoride (CsF), calcium fluoride (CaF₂), or the like canalso be used as a substance which shows an electron-donating property.

The first electrode 101 can be formed from a substance having a highwork function, such as indium tin oxide, indium tin oxide containingsilicon oxide, indium oxide containing zinc oxide of 2 wt % to 20 wt %,gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),tantalum nitride, or the like.

The second electrode 102 may be also formed from a material having ahigh work function, such as indium tin oxide, indium tin oxidecontaining silicon oxide, indium oxide containing zinc oxide of 2 wt %to 20 wt %, gold (Au), platinum (Pt), nickel (Ni), tungsten (W),chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu),palladium (Pd), tantalum nitride, or the like, or may be formed from asubstance having a low work function such as aluminum or magnesium.

The light emitting element shown in this embodiment can be formed bysequentially stacking from the first electrode or the second electrodeusing a known film formation method. In particular, the composite layercan be formed by co-evaporating in the manner that both of a conjugatedmolecule and an electron-accepting substance are vaporized by resistanceheating. Alternatively, the composite layer may be formed byco-evaporating in the manner that a conjugated molecule is vaporized byresistance heating and an electron-accepting substance is vaporized byelectron beam (EB). Also, the following method can be given: aconjugated molecule is vaporized by resistance heating and anelectron-accepting substance is sputtered, then both of them aresimultaneously deposited. In addition, a dry type method may beemployed.

Similarly, the first electrode 101 and the second electrode 102 can beformed by a vapor deposition method by resistance heating, EBdeposition, sputtering, wet type method, or the like.

In the case of forming sequentially from the second electrode 102 andforming the first electrode 101 by sputtering, there is a problem ofsputtering damage to a layer placed below the first electrode. However,the composite layer is not easily damaged by sputtering and serves as aprotective film which protects a light emitting layer from sputteringdamage in case of a structure shown in each of FIG. 1A and FIG. 1C sincethe composite layer is harder than an organic film. Accordingly, a lightemitting element with fewer defects can be obtained.

Embodiment 2

This embodiment is explained with reference to FIG. 2.

FIG. 2 shows a light emitting element including a first layer 211 whichis in contact with a first electrode 201, a second layer 212 which is incontact with the first layer 211, and a third layer 213 which is incontact with the second layer 212 and a second electrode 202 between thefirst electrode 201 and the second electrode 202. The light emittingelement in FIG. 2 emits light when voltage is applied so that anelectric potential of the first electrode 201 is higher than an electricpotential of the second electrode 202. The second layer 212 is a lightemitting layer and the first layer 211 is a layer having a function oftransporting or injecting a hole to the light emitting layer which isthe second layer. The first layer may have a hole injecting layer or ahole transport layer. A material illustrated in Embodiment 1 can be usedas a light emitting material, a material for the first electrode and thesecond electrode, an electron transporting material, a hole transportmaterial, and a hole injection material in this embodiment.

The third layer 213 includes a composite layer 214 at a second electrode202 side, and an electron generation layer 215 at a second layer 212side. A layer such as an electron transport layer may be eitherinterposed or not between the electron generation layer 215 and thesecond layer 212.

The electron generation layer 215 can be formed by mixing at least onesubstance selected from a substance having a high electron transportingproperty and a bipolar substance with a substance which shows anelectron-donating property to these substances. In particular, asubstance having electron mobility of 1×10⁻⁶ cm²/Vs or more ispreferable among a substance having a high electron transportingproperty and a bipolar substance. As for the substance having a highelectron transporting property and the bipolar substance, a substancedescribed above can be used. As a substance which shows anelectron-donating property, a substance selected from alkali metal oralkaline earth metal, specifically, lithium (Li), calcium (Ca), sodium(Na), potassium (K), magnesium (Mg), or the like can be used. Inaddition, alkali metal oxide or alkaline earth metal oxide, alkali metalnitride, alkaline earth metal nitride, alkali metal fluoride, alkalineearth metal fluoride, or the like, specifically, lithium oxide (Li₂O),calcium oxide (CaO), sodium oxide (Na₂O), potassium oxide (K₂O),magnesium oxide (MgO), magnesium nitride (Mg₃N₂), lithium fluoride(LiF), cesium fluoride (CsF), calcium fluoride (CaF₂), or the like canalso be used as a substance which shows an electron-donating property.

In accordance with the structure of this embodiment, the composite layer214 can be disposed between the second layer 212 which is a lightemitting layer and the second electrode 202. The composite layer 214 isa film having high conductivity; therefore, the composite layer can bethickened, and accordingly, short-circuit between the electrodes can beprevented and a light emitting element having high light extractionefficiency can be obtained. Further, the composite layer is difficult tobe crystallized; therefore, a light emitting element having lessoperation failure due to crystallization of a layer can be obtained.

Whether or not a hole transport layer is provided in the first layer 211or an electron transport layer is provided between the electrongeneration layer 215 and the second layer 212 may be appropriatelyselected by a practitioner. For example, these layers are notnecessarily provided in the case or the like where inconvenience such asquenching due to metal is not occurred even when a hole transport layeror an electron transport layer is not provided.

A light emitting element shown in this embodiment can be formed by aknown film formation method as well as a manufacturing method shown inEmbodiment 1.

When depositing is conducted sequentially from the first electrode 201and the second electrode 202 is deposited by sputtering, there is aproblem of sputtering damage to a layer placed below the secondelectrode. However, the composite layer 214 is harder than an organicfilm; therefore, the composite layer is not easily damaged by sputteringand serves as a protective film which protects a light emitting layerfrom sputtering damage. Accordingly, a light emitting element with fewerdefects can be obtained.

Embodiment 3

In this embodiment, a multilayer structure between a second layer 112and a first electrode 101 shown in Embodiment 1 and a multilayerstructure between a second layer 212 and a second electrode 202 shown inEmbodiment 2 are combined.

In this case, a composite layer is arranged between a first electrodeand a light emitting layer and between a second electrode and the lightemitting layer; accordingly, a light emitting element having higherconductivity and having a high hole injecting property or a high holetransporting property can be provided. In other words, a light emittingelement having an advantage of Embodiment 1 and an advantage ofEmbodiment 2 is obtained.

FIGS. 3A to 3C show a light emitting element which is one mode of thisembodiment. In FIGS. 3A to 3C, a second layer 312 which is a lightemitting layer is arranged between a first electrode 301 and a secondelectrode 302, which are a pair of electrode; a first layer 311, betweenthe first electrode 301 and the second layer 312; and a third layer 313,between the second electrode 302 and the second layer 312. The thirdlayer includes a first composite layer 324 which is at a secondelectrode 302 side and an electron generation layer 325 which is at asecond layer 312 side. The element shown in FIGS. 3A to 3C is a lightemitting element which emits light when voltage is applied to anelectrode so that an electric potential of the first electrode 301 ishigher than an electric potential of the second electrode 302.

FIG. 3A is a structure combining FIG. 1A and FIG. 2. A first layer 311in FIG. 3A includes a hole transport layer 326 at a second layer 312side and includes a composite layer 327 at a first electrode 301 side.

FIG. 3B shows a structure combining FIG. 1B and FIG. 2. A first layer311 in FIG. 3B includes a second composite layer 328 at a second layerside and includes a hole injecting layer 329 at a first electrode 301side.

FIG. 3C shows a structure combining FIG. 1C and FIG. 2. A first layer311 in FIG. 3C is a second composite layer 330.

In this embodiment, a composite of a conjugated molecule and anelectron-accepting substance, which is included in the first compositelayer and the second composite layer, may be either the same ordifferent. The light emitting element in this embodiment can be providedwith the composite layer in both of the first layer 311 and the thirdlayer 313; therefore, an element having high conductivity and high lightextraction efficiency can be obtained. In addition, when a firstelectrode or a second electrode is formed by sputtering, there is aproblem of sputtering damage to a layer placed in a lower layer.However, a composite layer is formed so as to be in contact with thefirst electrode and the second electrode in the structure shown in FIG.3A or FIG. 3C; therefore, sputtering damage associated with theformation of the first electrode or the second electrode can beprevented.

Although an electron transport layer is not provided between theelectron generation layer 325 and the second layer 312 in FIGS. 3A to3C, whether the electron transport layer is provided or not may beappropriately selected by a practitioner.

Embodiment 4

A light emitting element of the present invention can be used for apixel of a display device or a light source. In the case of using alight emitting element for a pixel, an image which has no operationfailure and has favorable display color can be displayed. Further, adisplay device or a light emitting device having high reliability can beprovided. Alternatively, in the case of using a light emitting elementfor a light source, a light emitting device having less inconveniencedue to operation failure of a light emitting element and exhibitingbright light emission can be obtained.

In this embodiment, a light emitting device including a light emittingelement of the invention in a pixel and having a display function isexplained.

FIG. 4 is a schematic top view of the light emitting device. In FIG. 4,a pixel portion 6511 using a light emitting element of the invention, asource signal line driver circuit 6512, a writing gate signal linedriver circuit 6513, and an erasing gate signal line driver circuit 6514are provided over a substrate 6500. The source signal line drivercircuit 6512, the writing gate signal line driver circuit 6513, and theerasing gate signal line driver circuit 6514 each are connected to anFPC (flexible printed circuit) 6503 which is an external input terminal,respectively, through a group of wirings. The source signal line drivercircuit 6512, the writing gate signal line driver circuit 6513, and theerasing gate signal line driver circuit 6514 receive a video signal, aclock signal, a start signal, a reset signal, and the like,respectively, through the FPC 6503. A printed wiring board (PWB) 6504 isattached to the FPC 6503. A driver circuit portion is not required to beprovided over the same substrate as the pixel portion 6511 as describedabove. For example, the driver circuit portion may be provided outsidethe substrate utilizing a TPC or the like which is formed by mounting anIC chip on an FPC provided with a wiring pattern.

In the pixel portion 6511, a plurality of source signal lines extendedin a column direction is arranged in a row direction and current supplylines are arranged in the row direction. In the pixel portion 6511, aplurality of gate signal lines extended in the row direction is arrangedin the column direction. Further, in the pixel portion 6511, a pluralityof pixel circuits including the light emitting element shown inEmbodiments 1 to 3 is arranged.

FIG. 5 is a diagram showing a circuit for making one pixel operate. Afirst transistor 901, a second transistor 902, and a light emittingelement 903 of the invention are included in the circuit shown in FIG.5.

The first transistor 901 and the second transistor 902 each have threeterminals including a gate electrode, a drain region, and a sourceregion and have a channel region between the drain region and the sourceregion. Here, since the source region and the drain region aredetermined depending on the structure, the operation condition, or thelike of the transistor, it is difficult to confine which is the sourceregion or the drain region. Therefore, in this embodiment, regions whichserve as a source or a drain are respectively referred to as a firstelectrode or a second electrode.

A gate signal line 911 and a writing gate signal line driver circuit 913are provided so as to be electrically connected or disconnected to eachother through a switch 918. The gate signal line 911 and an erasing gatesignal line driver circuit 914 are provided so as to be electricallyconnected or disconnected to each other through a switch 919. A sourcesignal line 912 is provided so as to be electrically connected to any ofa source signal line driver circuit 915 and a power source 916 through aswitch 920. A gate of the first transistor 901 is electrically connectedto the gate signal line 911. A first electrode of the first transistor901 is electrically connected to the source signal line 912 and a secondelectrode thereof is electrically connected to a gate electrode of thesecond transistor 902. A first electrode of the second transistor 902 iselectrically connected to a current supply line 917, and a secondelectrode thereof is electrically connected to one electrode included inthe light emitting element 903. Further, the switch 918 may be includedin the writing gate signal line driver circuit 913. The switch 919 maybe also included in the erasing gate signal line driver circuit 914. Inaddition, the switch 920 may be also included in the source signal linedriver circuit 915.

The arrangement of the transistor, the light emitting element, or thelike in the pixel portion is not limited in particular; however, thetransistor, the light emitting element, or the like can be arranged, forexample, as shown in a top view of FIG. 6. In FIG. 6, a first electrodeof a first transistor 1001 is connected to a source signal line 1004,and a second electrode thereof is connected to a gate electrode of asecond transistor 1002. A first electrode of the second transistor 1002is connected to a current supply line 1005, and a second electrodethereof is connected to an electrode 1006 of the light emitting element.A part of a gate signal line 1003 serves as a gate electrode of thefirst transistor 1001.

Embodiment 5

One mode of a light emitting device including a light emitting elementof the present invention is explained with reference to FIGS. 7A to 7Cand FIG. 8.

In each of FIGS. 7A to 7C, a transistor 11 is provided to drive a lightemitting element 12 of the invention. The light emitting element 12 is alight emitting element of the invention having a layer 15 in which atleast a composite layer and a layer containing a light emittingsubstance are stacked between a first electrode 13 and a secondelectrode 14. A drain of the transistor 11 is electrically connected tothe first electrode 13 through a wiring 17 which penetrates firstinterlayer insulating films 16 a, 16 b, and 16 c. The light emittingelement 12 is separated from another light emitting element which isprovided adjacent to the light emitting element 12 by a partition layer18. A light emitting device of the invention having such a structure isprovided over a substrate 10 in this embodiment.

The transistor 11 shown in each of FIGS. 7A to 7C is a top gate typetransistor in which a gate electrode is provided to the side opposite tothe substrate so as to interpose a semiconductor layer between the gateelectrode and the substrate. However, the structure of the transistor 11is not limited in particular, and for example, bottom gate typetransistor may be used. In case of a bottom gate type transistor, atransistor in which a protective film is formed over a semiconductorlayer which is to form a channel (channel protection type transistor) ora transistor in which a part of a semiconductor layer which is to form achannel has a depression shape (channel etch type transistor) may beused. Reference numeral 21 denotes a gate electrode; 22, a gateinsulating film; and 23, a semiconductor layer.

A semiconductor layer included in the transistor 11 may be any of acrystalline semiconductor, an amorphous semiconductor, a semi-amorphoussemiconductor, and the like.

A semi-amorphous semiconductor is described as follows. A semi-amorphoussemiconductor has an intermediate structure between an amorphousstructure and a crystalline structure (including a single crystallineand polycrystalline structure), a third state which is stable in termsof free energy, and a crystalline region having a short-range order andlattice distortion. In addition, at least a part of the film includes acrystal grain having a grain diameter of from 0.5 nm to 20 nm. The Ramanspectrum shifts to the lower wavenumber side than 520 cm⁻¹. Diffractionpeaks of (111) and (220) which is thought to be derived from Sicrystalline lattice are observed by X-ray diffraction. At least 1 atomic% or more of hydrogen or halogen is contained in the semi-amorphoussemiconductor in order to terminate a dangling bond. The semi-amorphoussemiconductor is also referred to as a so-called microcrystalsemiconductor. It is formed by glow discharge decomposition (plasma CVD)of a silicon source gas. SiH₄, additionally, Si₂H₆, SiH₂Cl₂, SiHCl₃,SiCl₄, SiF₄, or the like can be used as the silicon source gas. Thesilicon source gas may be diluted with H₂, or H₂ and one or more kindsof rare gas elements selected from He, Ar, Kr, or Ne. Dilution ratio isin the range of from 2 times to 1000 times. Pressure is in the range ofapproximately from 0.1 Pa to 133 Pa, and power frequency is from 1 MHzto 120 MHz, preferably, from 13 MHz to 60 MHz. The temperature forheating a substrate may be 300° C. or less, preferably, in the range offrom 100° C. to 250° C. As for an impurity element in the film,impurities of atmospheric component such as oxygen, nitrogen, or carbonare preferably set to be 1×10²⁰ cm³ or less, in particular, the oxygenconcentration is set to be 5×10¹⁹/cm³ or less, preferably, 1×10¹⁹/cm³ orless. Further, mobility of a TFT (thin film transistor) using asemi-amorphous semiconductor is approximately from 1 m²/Vsec to 10m²/Vsec.

As a specific example of a crystalline semiconductor layer, asemiconductor layer formed from single crystal silicon, polycrystallinesilicon, silicon germanium, or the like can be cited. These materialsmay be formed by laser crystallization. For example, these materials maybe formed by crystallization with use of a solid phase growth methodusing nickel or the like.

When a semiconductor layer is formed from an amorphous material, forexample amorphous silicon, it is preferable to use a light emittingdevice with circuits including only n-channel transistors as thetransistor 11 and another transistor (transistor included in a circuitfor driving a light emitting element). Alternatively, a light emittingdevice with circuits including any one of n-channel transistors andp-channel transistors may be employed. Also, a light emitting devicewith circuits including both an n-channel transistor and a p-channeltransistor may be used.

The first interlayer insulating films 16 a to 16 c may include plurallayers as shown in FIGS. 7A to 7C or a single layer. The firstinterlayer insulating film 16 a is formed from an inorganic materialsuch as silicon oxide and silicon nitride. The first interlayerinsulating film 16 b is formed from acrylic, siloxane (siloxane iscomposed of a skeleton formed by the bond of silicon (Si) and oxygen(O), in which an organic group containing at least hydrogen (such asalkyl group or aromatic hydrocarbon) is included as a substituent.Alternatively, a fluoro group may be used as the substituent. Furtheralternatively, a fluoro group and an organic group containing at leasthydrogen may be used as the substituent.), or a substance with aself-planarizing property that can be formed by applying a liquid suchas silicon oxide. The first interlayer insulating film 16 c is formed ofa silicon nitride film containing argon (Ar). The substancesconstituting each of the layers are not particularly limited thereto,and substances other than the above-mentioned substances may beemployed. Alternatively, a layer formed from substance other than theabove-mentioned substances may be further combined. Accordingly, thefirst interlayer insulating film may be formed from both an inorganicmaterial and an organic material or formed of any one of an inorganicfilm and an organic film.

The edge portion of the partition layer 18 preferably has a shape inwhich the radius of curvature is continuously varied. The partitionlayer 18 is formed from acrylic, siloxane, resist, silicon oxide, or thelike. Further, the partition layer 18 may be formed of any one of orboth an inorganic film and an organic film.

FIGS. 7A and 7C show the structures in which only the first interlayerinsulating film 16 (16 c to 16 c) is interposed between the transistors11 and the light emitting elements 12. Alternatively, FIG. 7B shows thestructure provided with the first interlayer insulating film 16 (16 aand 16 b) and a second interlayer insulting film 19 (19 a and 19 b). Inthe light emitting device shown in FIG. 7B, the first electrode 13penetrates the second interlayer insulating films 19 (19 a and 19 b) tobe connected to the wiring 17.

The second interlayer insulating film 19 (19 a and 19 b) may includeplural layers or a single layer as well as the first interlayerinsulating film 16 (16 a to 16 c). The second interlayer insulating film19 a is formed from acrylic, siloxane, or a substance with aself-planarizing property that can be formed by applying a liquid suchas silicon oxide. The second interlayer insulating film 19 b is formedfrom a silicon nitride film containing argon (Ar). The substancesincluded in each of the second interlayer insulating layers are notparticularly limited thereto, and substances other than theabove-mentioned substances may be employed. Alternatively, a layerformed from a substance other than the above-mentioned substances may befurther combined. Accordingly, the second interlayer insulating film 19(19 a and 19 b) may be formed from both an inorganic material and anorganic material or formed of any one of inorganic and organic films.

When the first electrode and the second electrode are both formed from asubstance with a light transmitting property in the light emittingelement 12, light can be emitted from both a first electrode 13 side anda second electrode 14 side as shown in outline arrows in FIG. 7A Whenonly the second electrode 14 is formed from a substance with a lighttransmitting property, light can be emitted only from a second electrode14 side as shown in an outline arrow in FIG. 7B. In this case, the firstelectrode 13 is preferably formed from a material with high reflectanceor a film (reflection film) formed from a material with high reflectanceis preferably provided below the first electrode 13. When only the firstelectrode 13 is formed from a substance with a light transmittingproperty, light can be emitted only from a first electrode 13 side asshown in an outline arrow in FIG. 7C. In this case, the second electrode14 is preferably formed from a material with high reflectance or areflection film is preferably provided above the second electrode 14.

Moreover, the light emitting element 12 may have a structure in whichthe layer 15 is stacked so that the light emitting element operates whenvoltage is applied so that an electric potential of the second electrode14 is higher than an electric potential of the first electrode 13.Alternatively, the light emitting element 12 may have a structure inwhich the layer 15 is stacked so that the light emitting elementoperates when voltage is applied so that an electric potential of thesecond electrode 14 is lower than an electric potential of the firstelectrode 13. In the former case, the transistor 11 is an n-channeltransistor. In the latter case, the transistor 11 is a p-channeltransistor.

As described above, although an active type light emitting device whichcontrols driving of a light emitting element by a transistor isexplained in this embodiment, a passive type light emitting device whichcontrols driving of a light emitting element without providing anelement for driving, such as a transistor, in particular may be used.

FIG. 8 shows a perspective view of a passive type light emitting devicemanufactured by applying the invention. In FIG. 8, a layer 955 includingat least a layer containing a light emitting substance and a compositelayer is provided between an electrode 952 and an electrode 956 whichare intersect with each other over a substrate 951. The edge portion ofthe electrode 952 is covered with an insulating layer 953. A partitionlayer 954 is provided over the insulating layer 953. The cross sectionof the partition layer 954 in a direction of a short side has aninverted trapezoidal shape in which a base is shorter than an upperside. Thus, failure of a light emitting element due to staticelectricity or the like can be prevented by providing the partitionlayer 954. In addition, also in a passive type light emitting device,driving at low power consumption can be conducted by including a lightemitting element of the invention which operates at low drive voltage.

Embodiment 6

As for a light emitting device using the light emitting element of theinvention as a pixel, there is fewer display defects due to operationfailure of the light emitting element; therefore, display operation isfavorable. Further, an electronic apparatus with less misconception orthe like of a display image due to display defect can be obtained. Inaddition, a light emitting device using the light emitting element ofthe invention as a light source can illuminate favorably with lessinconvenience due to operation failure of the light emitting element. Byusing such a light emitting device as an illuminating portion such as abacklight, operation failure such as the local formation of a darkportion due to inconvenience of the light emitting element is reduced.

FIGS. 9A to 9C show one example of an electronic device mounted with alight emitting device to which the invention is applied.

FIG. 9A is a personal computer manufactured by applying the invention,which includes a main body 5521, a chassis 5522, a display portion 5523,a keyboard 5524, and the like. A personal computer can be completed byincorporating a light emitting device shown in FIGS. 7A to 7C as adisplay portion. A personal computer can be also completed even when alight emitting device in which a light emitting element according to theinvention is used as a light source is incorporated as a backlight.Specifically, as shown in FIG. 10, a liquid crystal device 5512 and alight emitting device 5513 as a light source may be incorporated betweena chassis 5511 and a chassis 5514. The light emitting device 5513includes an array 5518 composed of a light emitting element according tothe invention and a light conducting plate 5517. In FIG. 10, an externalinput terminal 5515 is mounted on the liquid crystal device 5512 and anexternal input terminal 5516 is mounted on the array 5518.

FIG. 9B is a telephone set manufactured by applying the invention, and amain body 5552 includes a display portion 5551, an audio output portion5554, an audio input portion 5555, an operation switch 5556, anoperation switch 5557, an antenna 5553, and the like. A telephone setcan be completed by incorporating a light emitting device of theinvention as a display portion.

FIG. 9C is a television receiver manufactured by applying the invention,which includes a display portion 5531, a chassis 5532, a speaker 5533,and the like. A television receiver can be completed by incorporating alight emitting device of the invention as a display portion.

As described above, light emitting devices according to the inventionare much suitable for being used as display portions of variouselectronic devices. An electronic device is not limited to theelectronic device described in this embodiment, and may be anotherelectronic device such as a navigation system.

Embodiment 7

In this embodiment, a composite used as a material of a light emittingelement of the present invention is described. The composite is anobject in which any of conjugated molecules shown in general formulas[1] to [5] which will be described below with a substance having anelectron-accepting property to the conjugated molecule.

wherein X is the same as or different from Z, and X and Z each representany of a sulfur atom, an oxygen atom, a nitrogen atom to which hydrogen,an alkyl group, or an aryl group is bonded, and a silicon atom to whichhydrogen, alkyl group, or an aryl group is bonded; Y represents anarylene group; and R¹ to R⁶ each represent any of hydrogen, an arylgroup, an alkyl group, a cyano group, a dialkylamino group, a thioalkoxygroup, and an alkoxy group.

wherein Y represents an arylene group, and R¹ to R⁶ each represent anyof hydrogen, an aryl group, an alkyl group, a cyano group, adialkylamino group, a thioalkoxy group, and an alkoxy group.

wherein Y represents an arylene group, and R¹ to R⁶ each represent anyof hydrogen, an aryl group, an alkyl group, a cyano group, adialkylamino group, a thioalkoxy group, and an alkoxy group.

wherein Y represents an arylene group; R¹ to R⁶ each represent any ofhydrogen, an aryl group, an alkyl group, a cyano group, a dialkylaminogroup, a thioalkoxy group, and an alkoxy group; and R⁷ and R⁸ eachrepresent any of hydrogen, an alkyl group, and an aryl group.

wherein Y represents an arylene group; R¹ to R⁶ each represent any ofhydrogen, an aryl group, an alkyl group, a cyano group, a dialkylaminogroup, a thioalkoxy group, and an alkoxy group; and R⁷ to R¹⁰ eachrepresent any of hydrogen, an alkyl group, and an aryl group.

As for the conjugated molecules shown in general formulas [1] to [5]described above, in the formula, Y represents an arylene group andrepresents a bivalent aromatic hydrocarbon radical having a carbonnumber of 6 to 20 or a bivalent heteroaromatic ring radical having acarbon number of 4 to 30 including oxygen, nitrogen, sulfur, or silicon.

These conjugated molecules have extremely low ionization potential;therefore, an electron is transferred inside a composite by forming anelectron-accepting substance and a composite. Therefore, a compositelayer formed of a composite has a feature that a hole is easy togenerate or a hole is easy to move. In addition, due to such a feature,the composite layer has a feature of having high conductivity.Therefore, the composite layer is a layer in which a hole flows morefavorable since the composite layer has an electron-accepting substancewhen a layer including a material having low ionization potential iscompared with the composite layer.

Metal oxide or metal nitride is preferably used for theelectron-accepting substance. In particular, oxide having a transitionmetal which belongs to any of Groups 4 to 12 in the periodic table has ahigh electron-accepting property. In addition, there are many oxideseach having a transition metal which belongs to any of Groups 4 to 8 inthe periodic table having a further higher electron-accepting property.In particular, vanadium oxide, molybdenum oxide, rhenium oxide, tungstenoxide, ruthenium oxide, titanium oxide, chromium oxide, zirconium oxide,hafnium oxide, tantalum oxide, or niobium oxide is preferable.

Further, an organic compound having an electron-accepting property maybe used as the electron-accepting substance. Specifically,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethan (F4-TCNQ),chloranil, and the like are given. Further, Lewis acid may be used asthe electron-accepting substance. As an example of Lewis acid, FeCl₃(iron chloride (III)) and AlCl₃ (aluminum chloride) are given.

The most suitable mixture ratio of the electron-accepting substance inthe composite layer to any of the conjugated molecules represented bygeneral formulas [1] to [5] is as follows: electron-acceptingsubstance/conjugated molecule=0.1 to 10, preferably 0.5 to 2, at a molarratio. At this mixture ratio, an electron is efficiently transferredbetween the electron-accepting substance and the conjugated molecule andthe highest conductivity of the composite layer is obtained.

EXAMPLE 1

In this example, as a representative of a compound represented by ageneral formula [2], 1,4-di(3,4-ethylenedioxy-2-thienyl)benzene which isa compound represented by the following formula [6] and4,4′-di(3,4-ethylenedioxy-2-thienyl) biphenyl which is a compoundrepresented by the following formula [7] each were synthesized.

The compounds represented by formulas [6] and [7] have extremely lowionization potential. In other words, it is revealed that an effectiveconjugate length of the whole molecules is expanded by forming a cyclicstructure by R¹ and R² and forming a cyclic structure by R³ and R⁴ inthe compounds represented by the general formulas [1] to [5].

FIG. 11 shows ultraviolet-visible absorption spectrum of1,4-di(3,4-ethylenedioxy-2-thienyl)benzene (formula [6]) and itsanalogue, 1,4-bis(3,4-dihexyloxy-2-thienyl)benzene. Formula [8] shows astructure of 1,4-bis(3,4-dihexyloxy-2-thienyl)benzene. An absorptionmaximum of the former compound is at 380 nm as shown in (A) in FIG. 11,while an absorption maximum of the latter compound is at 300 nm as shownin (B) in FIG. 11, thereby revealing that the formula [6] which has thecyclic structure has a conjugated system which is expanded more. Asshown in (A) in FIG. 11, absorption intensity in the visible lightregion of the formula [6] is remarkably low, and this is prominentlydifferent from a conventional hole injection material.

Further, a cyclic voltammetry measurement is conducted by the formulas[6] and [8]. From the measurement thereof, it is revealed that theformula [6] has a conjugated system which is expanded more. The cyclicvoltammetry measurement is conducted by using acetonitrile as a solventand tetrabutyl ammonium perchlorate as a supporting electrolyte. Each ofa working electrode and a counter electrode is formed from platinum.Silver/silver chloride is used for a reference electrode.

Accordingly, oxidation potential of the formula [8] is 1.68 V, whileoxidation potential of the formula [6] is 1.20 V (vs. Ag/Ag⁺), therebyrevealing that the formula [8] is less subject to oxidation.

To sum up, an effective conjugate length of the whole molecules isexpanded by forming a cyclic structure by R¹ and R² and forming a cyclicstructure by R³ and R⁴ in the conjugated molecules represented by thegeneral formulas [1] to [5]. When an effective conjugate length isexpanded, a band gap is shortened and ionization potential is lowered.Therefore, an electron-donating property of a conjugated molecule ismore heightened. Accordingly, a composite layer having higherconductivity, in which a hole is generated more easily, is obtained byforming a composite layer from a conjugated molecule in which aneffective conjugate length is expanded, and an electron-acceptingsubstance.

EXAMPLE 2

In this example, the synthesis of1,4-di(3,4-ethylenedioxy-5-trimethylsilyl-2-thienyl)benzene representedby the following formula [9] as a representative of a compoundrepresented by a general formula [2] is described.

FIGS. 12A to 12D show the synthesis scheme. A hexane solution (48 ml,74.9 mmol) of 1.56N n-butyllithium is dropped into a dry THF solution(100 mL) of 3,4-ethylenedioxythiophene (compound in FIG. 12A; 10.30 g,72.5 mmol) at −78° C. After completion of the dropping, the solution isstirred for one hour at −78° C. Chlorotrimethylsilane (8.93 g, 82.3mmol) is dropped into the solution and a temperature of the reactedsolution is gradually raised to a room temperature. After stirring forthree hours, the reacted mixture is concentrated under reduced pressure,followed by extraction with hexane. A hexane layer is dried withmagnesium sulfate, followed by filtering. The filtered object isconcentrated, and then a residue is distilled under reduced pressure(200 Pa, 94° C. to 100° C.), thereby giving2-trimethylsilyl-3,4-ethylenedioxythiophene which is a compoundrepresented by FIG. 12B. Yield: 84%.

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (300 MHz, CDCl₃) δ 0.286 (s, 9H), 4.16 (s, 2H), 4.17 (s, 2H),6.54 (s, 1H): ¹³C NMR (75 MHz, CDCl₃) δ −0.74, 64.42, 64.51, 104.68,111.28, 142.63, 147.25.

A hexane solution (55 mL, 86.0 mmol) of 1.56N n-butyllithium is droppedinto a dry THF solution (150 mL) of the compound represented by FIG.12B, 2-trimethylsilyl-3,4-ethylenedioxythiophene (18.6 g, 86.0 mmol), at−78° C. After completion of the dropping, the mixture is stirred for onehour at −78° C. and for 30 minutes at 0° C. This solution is droppedinto a dry THF suspension (100 mL) of zinc chloride (11.69 g, 85.8 mmol)at a room temperature. After stirring for one hour, a compoundrepresented by FIG. 12C is obtained in the system. After that,1,4-diburomobenzene (6.759 g, 28.7 mmol) andtetrakis(triphenylphosphine)palladium (0) (1.28 g, 1.11 mmol) are added,followed by heat-reflux for ten hours. The reacted mixture is throwninto water of approximately 1 L, and then precipitates are filtered. Thefiltered object is dried and then purified by silica gel columnchromatography (developer: hexane/ethyl acetate 10/1 to 2/1), followedby recrystallization with hexane/ethyl acetate (5/1), thereby giving1,4-di(3,4-ethylenedioxy-5-trimethylsilyl-2-thienyl)benzene which is acompound represented by FIG. 12D. Yield: 43%.

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (300 MHz, CDCl₃) δ 0.311 (s, 18H), 4.27 (s, 4H), 4.29 (s, 4H),7.69 (s, 4H).

FIG. 13 shows an ultraviolet-visible absorption spectrum of thethus-synthesized compound represented by FIG. 12D. As shown in FIG. 13,the absorption in a visible light region is remarkably small, and,thanks to the small absorption, it is possible to largely reduce thecoloring of the element.

EXAMPLE 3

In this example, an effect of introducing a substituent other thanhydrogen into R⁵ and R⁶ in the compounds represented by general formulas[1] to [5] is described. Solubility is remarkably low when R⁵ and R⁶ arehydrogen atoms. For instance, solubility to chloroform of the compoundrepresented by the formula [6] described in Example 1 is less than 1 wt% at 25° C. In contrast, in the case where R⁵ and R⁶ represented by FIG.12D are trimethylsilyl groups, the solubility to chloroform at 25° C. is15.4 wt %. Thus, it is possible to considerably improve the solubilityby introducing the substituent other than hydrogen into R⁵ and R⁶.

Further, solubility is low when hydrogen is introduced into R⁵ and R⁶;however, when a substituent other than hydrogen is introduced, adeposited film having favorable film quality is obtained in a reflectionof high solubility.

EXAMPLE 4

In this example, the synthesis of4,4′-bis(5-phenyl-3,4-ethylenedioxy-2-thienyl) biphenyl (hereinafter,referred to as DPEBP) represented by the following formula [10] as arepresentative of a compound represented by a general formula [2] isdescribed.

First, the synthesis of the following formula [11] which is anintermediate (hereinafter, referred to as “intermediate a”) isdescribed. A dry THF solution of 250 ml is added into2,3-dihydrothieno-[3,4-b]-1,4-dioxin of 22.41 g, followed by cooling to−78° C. Then, n-butyllithium (hexane solution of 1.58M) of 100 ml isdropped, followed by stir for one hour. The obtained mixture is addedinto zinc chloride of 25.84 g at a room temperature, and then furtherstirred at a room temperature for one hour. Bromobenzene of 18.3 ml andtetrakis(triphenylphosphine)palladium of 1.83 g are added into thismixture, and then stirred for five hours under heat-reflux. Ethylacetate, hydrochloric acid of 1M, and water are added into the solutioncooled up to a room temperature, followed by fractionation of an organiclayer. After drying by magnesium sulfate, the solvent is concentrated.Then, purification is conducted by column chromatography (hexane/ethylacetate).

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (CDCl₃, δ) 7.72 ppm (d, 2H), 7.36 ppm (t, 2H), 7.21 ppm (t, 1H),6.29 ppm (s, 1H), 4.29 ppm (m, 4H).

Next, a THF of 100 ml is added into the obtained intermediate a of 10.36g, followed by cooling to −78° C. Then, n-butyllithium (hexane solutionof 1.58M) of 33.1 ml is dropped, followed by stir for one hour. Theobtained mixture is added into zinc chloride of 7.77 g at a roomtemperature, and further stirred at a room temperature for one hour.4,4′-diiodo biphenyl of 8.77 g and tetrakis(triphenylphosphine)palladiumof 549 mg are added into the mixture, and then stirred for five hoursunder heat-reflux. A solid obtained by filtering this mixture is washedwith ethanol. Recrystallization is conducted using chloroform, followedby obtaining an organic compound DPEBP (yellow powder) of the presentinvention.

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (CDCl₃, δ) 7.77 ppm (m, 12H), 7.44 ppm (t, 4H), 7.28 ppm (t, 2H),4.45 ppm (s, 8H).

EXAMPLE 5

In this example, the synthesis of1,4-bis(5-phenyl-3,4-ethylenedioxy-2-thienyl)benzene (hereinafter,referred to as DPEBZ) represented by the following formula [12] as arepresentative of a compound represented by a general formula [2] isdescribed.

A THF of 100 ml is added into the intermediate a 6.07 g obtained inExample 4, followed by cooling to −78° C. Then, n-butyllithium (hexanesolution of 1.58M) of 19.4 ml is dropped, followed by stir for one hour.The obtained mixture is added into zinc chloride of 4.50 g at a roomtemperature, and then further stirred at a room temperature for onehour. 1,4-diiodo benzene of 4.12 g andtetrakis(triphenylphosphine)palladium of 321 mg are added into themixture, and then stirred for five hours under heat-reflux. The solidobtained by filtering this mixture is washed with ethanol.Recrystallization is conducted using chloroform, followed by obtainingan organic compound DPEBZ (orange powder) of the present invention.

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (CDCl₃, δ) 7.77 ppm (m, 8H), 7.38 ppm (t, 4H), 7.23 ppm (t, 2H),4.38 ppm (s, 8H).

EXAMPLE 6

In this example, the synthesis of4,4′-bis[5-(4-tert-buthylphenyl)-3,4-ethylenedioxy-2-thienyl) biphenyl(hereinafter, referred to as DtBuPEBP) represented by the followingformula [13] as a representative of a compound represented by a generalformula [2] is described.

First, the synthesis of the following formula [14] which is anintermediate (hereinafter, referred to as “intermediate b”) isdescribed. A THF of 100 ml is added into2,3-dihydrothieno-[3,4-b]-1,4-dioxin of 10.57 g, followed by cooling to−78° C. A LDA (2.0M) of 37.2 ml is dropped, followed by further stirredfor one hour. Zinc chloride of 12.14 g is added, and then stirred at aroom temperature for one hour. 1-bromo-4-tert-butylbenzene of 14.3 mland tetrakis(triphenylphosphine)palladium of 859 mg are added into thismixture, followed by stirred under heat-reflux for eight hours. Ethylacetate and water are added into the solution cooled at a roomtemperature, followed by fractionation of an organic layer. After dryingby magnesium sulfate, the solvent is concentrated. Then, purification isconducted by column chromatography (toluene).

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (CDCl₃, δ) 7.67 ppm (d, 2H), 7.45 ppm (d, 2H), 6.32 ppm (s, 1H),1.40 ppm (s, 9H).

A THF of 50 ml is added into the intermediate b of 2.56 g obtainedabove, followed by cooling to −78° C. A LDA (2.0M) of 5.12 ml isdropped, followed by stir for one hour. Zinc chloride of 1.53 g isadded, and stirred at a room temperature for one hour. 4,4′-diiodobiphenyl of 1.71 g and tetrakis(triphenylphosphine)palladium of 107 mgwere added, and then stirred for six hours under heat-reflux. Ethylacetate, hydrochloric acid of 1M, and water are added into the solutioncooled to a room temperature, followed by fractionation of an organiclayer. After drying by magnesium sulfate, the solvent is concentrated.Recrystallization is conducted using chloroform, followed by obtainingan organic compound DtBuPEBP of the present invention.

The ¹H NMR spectrum of the product is obtained and the result is asfollows:

¹H NMR (CDCl₃, δ) 7.80 ppm (d, 4H), 7.66 ppm (m, 8H), 7.41 ppm (d, 4H),4.36 ppm (s, 8H), 1.32 ppm (s, 9H).

This application is based on Japanese Patent Application serial No.2004-347693 field in Japan Patent Office on Nov. 30, 2004, the entirecontents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCES

101: first electrode, 102: second electrode, 111: first layer, 112:second layer, 113: third layer, 114: composite layer, 115: holetransport layer, 116: composite layer, 117: hole injecting layer, 118:composite layer, 201: first electrode, 202: second electrode, 211: firstlayer, 212: second layer, 213: third layer, 214: composite layer, 215:electron generation layer, 301: first electrode, 302: second electrode,311: first layer, 312: second layer, 313: third layer, 324: firstcomposite layer, 325: electron generation layer, 326: hole transportlayer, 327: second composite layer, 328: second composite layer, 329:hole injecting layer, 330: second composite layer, 6500: substrate,6503: FPC, 6504: printed wiring board (PWB), 6511: pixel portion, 6512:source signal line driver circuit, 6513: writing gate signal line drivercircuit, 6514: erasing gate signal line driver circuit, 901: firsttransistor, 902: second transistor, 903: light emitting element, 911:gate signal line, 912: source signal line, 913: writing gate signal linedriver circuit, 914: erasing gate signal line driver circuit, 915:source signal line driver circuit, 916: power supply, 917: currentsupply line, 918: switch, 919: switch, 920: switch, 1001: firsttransistor, 1002: second transistor, 1003: gate signal line, 1004:source signal line, 1005: current supply line, 1006: electrode, 10:substrate, 11: transistor, 12: light emitting element, 13: firstelectrode, 14: second electrode, 15: layer, 16 a: first interlayerinsulating film, 16 b: first interlayer insulating film, 16 c: firstinterlayer insulating film, 17: wiring, 18: partition layer, 19 a:second interlayer insulating film, 19 b: second interlayer insulatingfilm, 21: gate electrode, 22: gate insulating film, 23: semiconductorlayer, 951: substrate, 952: electrode, 953: insulating layer, 954:partition layer, 955: layer, 956: electrode, 5521: main body, 5522:chassis, 5523 display portion, 5524: keyboard, 5551: display portion,5552: main body, 5553: antenna, 5554: audio output portion, 5555: audioinput portion, 5556: operation switch, 5557: operation switch, 5531:display portion, 5532: chassis, 5533: speaker, 5511: chassis, 5512:liquid crystal device, 5513: light emitting device, 5514: chassis, 5515:external input terminal, 5516: external input terminal, 5517: lightconducting plate, 5518: array, 1501: first electrode, 1502: secondelectrode, 1503: layer, 1511: hole transport layer, 1512: light emittinglayer, 1513: electron transport layer

1. A light emitting element comprising: a pair of electrodes including afirst electrode and a second electrode; a light emitting layer betweenthe pair of electrodes; and a layer between the light emitting layer andat least one of the pair of electrodes, wherein the layer contains acomposite of a conjugated molecule represented by a following generalformula [1] and a substance having an electron-accepting property to theconjugated molecule,

wherein the X is the same as or different from the Z, wherein the X andthe Z each represent a sulfur atom, an oxygen atom, a nitrogen atom towhich hydrogen, an alkyl group, or aryl group is bonded, or a siliconatom to which hydrogen, alkyl group, or aryl group is bonded, whereinthe Y represents an arylene group, and wherein the R¹ to R⁶ eachrepresent any of a hydrogen atom, an aryl group, an alkyl group, a cyanogroup, a dialkylamino group, a thioalkoxy group, and an alkoxy group. 2.A light emitting element comprising: a pair of electrodes including afirst electrode and a second electrode; a light emitting layer betweenthe pair of electrodes; and a layer between the light emitting layer andat least one of the pair of electrodes, wherein the layer contains acomposite of a conjugated molecule represented by a following generalformula [2] and a substance having an electron-accepting property to theconjugated molecule,

wherein the Y represents an arylene group, and wherein the R¹ to R⁶ eachrepresent any of a hydrogen atom, an aryl group, an alkyl group, a cyanogroup, a dialkylamino group, a thioalkoxy group, and an alkoxy group. 3.A light emitting element comprising: a pair of electrodes including afirst electrode and a second electrode; a light emitting layer betweenthe pair of electrodes; and a layer between the light emitting layer andat least one of the pair of electrodes, wherein the layer contains acomposite of a conjugated molecule represented by a following generalformula [3] and a substance having an electron-accepting property to theconjugated molecule,

wherein the Y represents an arylene group, and wherein the R¹ to R⁶ eachrepresent any of a hydrogen atom, an aryl group, an alkyl group, a cyanogroup, a dialkylamino group, a thioalkoxy group, and an alkoxy group. 4.A light emitting element comprising: a pair of electrodes including afirst electrode and a second electrode; a light emitting layer betweenthe pair of electrodes; and a layer between the light emitting layer andat least one of the pair of electrodes, wherein the layer contains acomposite of a conjugated molecule represented by a following generalformula [4] and a substance having an electron-accepting property to theconjugated molecule,

wherein the Y represents an arylene group, wherein the R¹ to R⁶ eachrepresent any of hydrogen, an aryl group, an alkyl group, a cyano group,a dialkylamino group, a thioalkoxy group, and an alkoxy group, andwherein the R⁷ and the R⁸ each represent any of hydrogen, an alkylgroup, and an aryl group.
 5. Alight emitting element comprising: a pairof electrodes including a first electrode and a second electrode; alight emitting layer between the pair of electrodes; and a layer betweenthe light emitting layer and at least one of the pair of electrodes,wherein the layer contains a composite of a conjugated moleculerepresented by a following general formula [5] and a substance having anelectron-accepting property to the conjugated molecule,

wherein the Y represents an arylene group, wherein the R¹ to R⁶ eachrepresent any of hydrogen, an aryl group, an alkyl group, a cyano group,a dialkylamino group, a thioalkoxy group, and an alkoxy group, andwherein the R⁷ to R¹⁰ each represent any of hydrogen, an alkyl group,and an aryl group.
 6. A light emitting element according to any one ofclaims 1 to 5, wherein the light emitting element emits light from thelight emitting layer when a voltage is applied so that an electricpotential of the first electrode is higher than that of the secondelectrode, and wherein the layer is between the first electrode and thelight emitting layer.
 7. A light emitting element according to any oneof claims 1 to 5, wherein the light emitting element emits light fromthe light emitting layer when a voltage is applied so that an electricpotential of the first electrode is higher than that of the secondelectrode, wherein the layer is between the second electrode and thelight emitting layer, and wherein the light emitting element has anelectron generation layer which is in contact with the layer at a lightemitting layer side.
 8. A light emitting element according to any one ofclaims 1 to 5, wherein the light emitting element emits light from thelight emitting layer when a voltage is applied so that an electricpotential of the first electrode is higher than that of the secondelectrode, wherein the layer is between the first electrode and thelight emitting layer, and between the second electrode and the lightemitting layer, and wherein the light emitting element has an electrongeneration layer which is in contact with the layer between the secondelectrode and the light emitting layer at a light emitting layer side.9. A light emitting element according to any one of claims 1 to 5,wherein the substance having the electron-accepting property to theconjugated molecule contains a metal oxide, a metal nitride, an organiccompound, or Lewis acid.
 10. A light emitting element according to anyone of claims 1 to 5, wherein the Y in the formula of the conjugatedmolecule contains a bivalent aromatic hydrocarbon radical having acarbon number of 6 to 20, or a bivalent heteroaromatic ring radicalhaving a carbon number of 4 to 30 including oxygen, nitrogen, sulfur orsilicon.
 11. A light emitting element according to any one of claims 1to 5, wherein a cyclic structure is formed by the R¹ and the R² of theconjugated molecule, and a cyclic structure is formed by the R³ and theR⁴.
 12. A light emitting element according to any one of claims 1 to 5,wherein the light emitting element is used as a pixel of an electronicapparatus.
 13. A light emitting element according to claim 12, whereinthe electronic apparatus is at least one selected from the groupconsisting of a personal computer, a telephone, and a television.
 14. Alight emitting element according to any one of claims 1 to 5, whereinthe light emitting element is used as a light source.